Results of Many-year Photometry of the Herbig Ae Star AB Aur in the Near Infrared

Abstract

The results of many-year infrared observations of the Herbig AeBe star AB Aur at 1-5 μm (JHKLM bands) are presented. The duration of the photometric series, together with observations published earlier, is about 18 years. The observations demonstrate that, in contrast to the optical, the star is quite active in the studied infrared range. The variability amplitude increases with wavelength, reaching ΔM = 0.72^m. Modeling shows that both the amount of IR radiation from the inner part of the disk and its temperature increase when the star becomes brighter. A periodogram analysis demonstrates that variations of the IR flux from AB Aur display significant evidence for periodic changes, whose stability is uncertain. This behavior is most probably associated with transient quasi-oscillations related to instability processes in the inner disk. The estimated correlation timescale, τ = 130 ± 40^d, can be considered as an approximate characteristic of the duration of such processes. The analysis results provide no certain grounds to believe that the inner disk contains any massive objects in permanent orbits, such as protoplanets. The existing trend in the variations of the IR flux, most clearly expressed in the KLM bands, provides evidence for the presence of large-scale perturbations in the disk. Conditions that could bring about a cyclic character in the accretion of gas from the circumstellar disk onto the young star are briefly discussed.